Several parameters (egg passage with excreta, urine cytology as a technic to document bladder pathology, urogenital system x-ray, cystotomy, electron microscopy of bladder biopsies) have been employed to follow the basic parasitology of experimental schistosomiasis haematobia in nonhuman primates, with particular attention directed to the Schistosoma haematobium-capuchin monkey (Cebus apella) system in which a causal relationship between bladder cancer and S. haematobium infection has been established. Extensive bladder involvement, including precancerous lesions and cancer in situ, has been observed in a number of hosts, but no deep tissue penetration or metastasis has been demonstrated. Since a relationship between duration of infection and bladder pathology was suspected, infected primates have been monitored for 5 plus years. Accumulated information has allowed publication of a number of ancillary reports on schistosome biology. All study subjects will be sacrificed in the near future, histopathologic evaluations made, with emphasis on urogenital systen involvement, and in the final year additional reports will be prepared on the biology of S. haematobium infection as related to bladder pathology.